Method for detecting multi-user behavior of an aerial interface in gprs and egprs mobile radio system

ABSTRACT

Method and apparatus for detecting multiuser behavior on the aerial interface in GPRS and EGPRS mobile radio systems, wherein during a transmission of subscriber data on the aerial interface, additional information contained in the subscriber data are acquired and evaluated by a device on the network side and/or the subscriber side, both in the uplink and the downlink. The number of parallel subscribers on used time slots can be identifies on the basis of the additional information located in the radio control blocks.

The invention relates to a method for detecting on the subscriber sideor on the network side multiuser behavior on an aerial interface in GPRSand EGPRS mobile radio system.

GPRS is an abbreviation for General Packet Radio Service (EGPRS:Enhanced GPRS) and enables for the first time GSM mobile radio networkoperators to offer packet-based data services without permanentlyallocating resources of the aerial interface. GPRS supports many datatransmission protocols of the higher-level OSI layers, for example IPand X.25. This enables the mobile radio subscriber to communicate withexternal data networks, for example the Internet and intranets insidecompanies. GPRS can allocate a single transmission channel (i.e.,timeslot) to several subscribers. Likewise, several timeslots can beallocated to a single subscriber for data transmission. The data to betransmitted are divided into packets (i.e., RLC blocks) and transmittedover the channel(s). With GPRS, the transmission capacity is shared byall GPRS subscribers of a radio cell. Special protocols in the radiolink are responsible for preventing collisions in the channel duringpacket allocation and for allocating the transmission capacity to thevarious subscribers. The BSS manufacturers employ functions developed byETSI as well as additionally proprietary functions.

Generally, for a more detailed discussion of GPRS and EGPRS, referenceis made to the published ETSI specifications applicable at the time ofthe filing for this patent.

FIG. 1 shows the architecture of a GPRS-enabled mobile communicationnetwork. The GPRS system is based on the so-called GPRS Support Nodes(GSN), which are responsible for packet switching and operate as agateway to other packet networks, such as the Internet 6 or Internet 7.The GSN's are also responsible for mobility management, i.e., foridentifying and monitoring the location of the subscribers. The GSN issubdivided into the SGSN and the GGSM. The Serving GPRS Support Note(SGSN) 1 is, inter alia, also responsible for mobility management andperforms for packet data services a function similar to that of theMobile Switching Center (MSC) 2 for the connection-enabled voicesignals. The SGSN can be connected to the MSC via the GS interface as anoptional interface. The MSC is connected via the Gateway MobileSwitching Center (GMSC) 3, for example, with the public switchedtelephone network (PSTN) 4. The Gateway GPRS Support Node (GGSN) 5performs, as a gateway, in GPRS networks the function of coordinatingthe data traffic between external packet-switching transmission networks6, 7 and the switching network of the mobile radio network. The SGSN 1and the GGSN 5 communicate via an IP backbone. The SGSN 1 sets up thedata communication with the radio network section. To accomplish this,the SGSN communicates via a Frame Relay network with the Packet ControlUnits (PCU) 8. The PCU 8 represents the GPRS-portion added in the BSS,transmitting data to and receiving data from the Based StationController (BSC) 9. The BSC 9 is already a component of the conventionalGSM network and establishes communication with the base stations (BTS)10. It is the main mission of the BSC 9 to generally administer theradio resources of the connected cells, whereby an internal resourcemanager, in conjunction with corresponding internal signaling means,allocates the required circuit-switched and packet-switched resourcesaccording to the requirements (=traffic demand), the available capacityand the applicable rules. Conventional “voice data” (circuit-switched)from a mobile radio terminal (ME) 11 are then transported from the BSC 9to the MSC 2 (solid connecting lines). Packet data are transported fromBSC 9 to SGSN1 via the PCU 8 (dashed connecting lines). The PCU 8 has tosatisfy two core functions for a coordinated packet data traffic forradio transmission, which are implemented by the MAC and the RLCprotocol layer. The RLC layer (Radio Link Control) segments the datapackets, which arrive from the SGSN 1 for the downlink and from ME forthe uplink, into several smaller sub-packets for transmission on theaerial interface, so that the data packets can be converted into therequired format (segmentation of the LLC frames into RLC blocks). Thesesmaller sub-packets are reassembled at the receiver into data packets(reassembly of the RLC blocks into LLC frames). All sub-packets areconsecutively numbered to enable the receiver to assemble thesub-packets again in the proper order. The MAC protocol layer (MediumAccess Control) controls access to the radio channel and allocation ofthe GPRS radio resources to several subscribers. In addition, the MAClayer also controls radio channel access and allocation of the GPRSradio resources to several subscribers. Moreover, the MAC layer alsocontrols termination of the radio resource allocation for a GPRSsubscriber.

Commensurate with the existing specifications, the quality of theoffered GPRS service is defined and measured by several features. One ofthese features is the achieved throughput (bit rate) during datatransmission.

In general, the entire transmission path has to be taken intoconsideration for the data throughput:

-   -   starting at the (Internet) server and the Internet    -   via the PSS with the GSN elements and the transmission paths    -   via the BSS with the PCU and the transmission paths    -   to the mobile end system (ME)

In a mobile radio network, the transmission path of the aerialinterface, i.e., from the BTS to the ME, is of particular importance.

The throughput on the aerial interface is affected by severalquantities:

-   -   by the multislot class (MSK) of the ME, i.e., the maximum data        rate supported by the terminal in receive and transmit        direction,    -   by the transmission capacity supplied by the provider,    -   in general, by the employed channel coding scheme, which is        determined by the existing C/I ratio and the system-intrinsic        decision threshold for a change of the protocol in particular        situations,    -   by the system-intrinsic allocation methods of the resource        aerial interface, and    -   if this resource is provided to a single subscriber or must be        shared with other subscribers (multiuser behavior)

Modern measurement, evaluation, and rating systems, subsequentlyreferred to simply as measurement systems, allow conclusions relating tothe used channel coding scheme and the number of the used timeslots.However, today's measurement systems lack the option of evaluating themultiuser behavior on the transmission channels (timeslots).

It is therefore an object of the invention to provide a method fordetecting multiuser behavior on the aerial interface in (E)GPRS mobileradio systems, which is capable of identifying and evaluating multiuserbehavior in the timeslots.

This object is solved with the invention by the features of claim 1.

Advantageous embodiments and modifications of the invention are recitedin the dependent claims.

The basic principle of the proposed solution is that during transmissionor reception of the subscriber data, the measurement systems collect andevaluate information on the aerial interface which allows conclusionsabout the multiuser behavior.

For a detailed evaluation, different mechanisms must be applied foruplink (UL) and downlink (DL), depending if the system is viewed fromthe subscriber side or from the network side.

The proposal is based on the basic concept of comparing the number ofactually used RLC blocks with the number of potentially available andhence usable RLC blocks, and to identify the number of other (parallel)subscribers in the used timeslots (for the subscriber side, for examplebased on the additional information contained in the RLC blocks), at thebeginning of the TBF (Temporary Blocks Flow), i.e., at the beginning ofthe transmission of packet data between the subscriber terminal and thePCU.

Unless noted otherwise, the term “RLC-Blocks” hereinafter describes thecategory of the RLC data blocks as well as the category of the RLC/MACcontrol blocks.

It should also be noted that cells can change during mobile datatransfer. Therefore, the evaluation must be performed, on one hand, foreach TFB, and on the other hand, as aggregation/combination of all TBF'sthat participate in the transfer.

Due to the possible multislot operation of the measurement system, themeasurement and evaluation modalities have to be designed accordingly.

The following description is organized in relation to the subscriberside and to the network side.

Subscriber Side

Method for the Uplink

The network side assigns the resource RLC blocks to the subscribers. Twodifferent methods are employed: the static and the dynamic allocationmethod; however, the dynamic allocation method is most commonly used.

With the dynamic allocation method, the ME is informed via the so-calledUplink State Flag (USF) in the DL-RLC blocks, which UL-RLC blocks therespective ME is allowed to use. This USF is listed in the MAC header ofeach DL-RCL data block and DL-RLC/MAC control block, which the mobileterminating systems must evaluate until all UL data have beentransmitted.

The USF is associated with the TBF, which is identified by the TFI, andhence also with the ME/subscriber in the so-called TBF EstablishmentProcess.

The subscriber-side measurement systems must determine at the beginningof the TBF, relative to the used timeslots, if all UL-RLC blocks wereoccupied only by that TBF until its end, or if other subscribers alsoused these UL-RLC blocks. The number of parallel, i.e., simultaneousME/subscribers can then be determined from the number of differentUSF's, allowing a conclusion about the multiuser behavior. Thisdetermination can also indicate the potential throughput.

With static allocation methods, an allocation is made by the messagePACKET_UL_ASSIGNMENT. Accordingly, this method can estimate the usage ofthe timeslots only by counting the RLC blocks.

Method for the Downlink

The network side also allocates the resources for the DL, usingdifferent methods of the respective BSS manufacturer. Again, TBF and TFIare allocated within the context of the TBF Establishment Process. TheTFI is used for detecting the multiuser behavior in the downlink. TheTFI is part of the DL-RLC header or the DL-RLC/MAC control block.

The subscriber-side measurement systems have to determine again from thebeginning of the TBF to the data transmission, if all DL-RLC blocks areused solely by this TFB/TFI, or not. This must be done for each usedtimeslot. This determination can again allow conclusions about themultiuser behavior.

In general, the same basic principles apply to EGPRS as well as to GPRS.The EGPRS data blocks include a RLC/MAC header which includes thecorresponding information. Unlike with GPRS, however, the header formatsand header types with EGPRS are different depending on the employedmodulation and coding scheme.

Network Side

Because BSC and PCU allocate resources on the aerial interface for boththe uplink and the downlink, specific information with respect to

-   -   the number of subscribers (TBF/TFI),    -   the allocation to the RLC blocks, and    -   the number and the allocation of the used transmission        channels/timeslots    -   is generally known.

A network-side measurement system must for each TBF/TFI combine theavailable specific information into all-inclusive information withrespect to the issues relating to a multiuser operation for therespective TBF/TFI. The same methods and processes are used for theuplink and the downlink.

The methods and processes known to date, as used for measuring andevaluating the quality and for analyzing potential system errors, havebeen inconclusive when assessing if the individual data throughput isreduced because several ME/subscribers simultaneously use the resource“timeslot.”

Conversely, by implementing the methods of the invention (bothseparately for each side and in combination) and by using these novelanalytical techniques for evaluation, it could be directly demonstrated,where a reasonable increase in the capacity can significantly improvethe quality for the subscriber in an efficient and demand-driven manner.

The quality analysis can be further improved, e.g., through combinationswith other evaluation methods, for example, through a combination withthe channel coding scheme used in all LC data blocks, or with themeasured receive level.

The invention will be described hereinafter with reference to thedrawings. Additional features, advantages and applications of theinvention can be inferred from the drawings and the correspondingdescription.

It is shown in:

FIG. 1 an architecture of a GSM-GPRS network;

FIG. 2 a format of a GPRS downlink RLC data block with MAC header;

FIG. 3 a format of a GPRS downlink RLC/MAC control block with MACheader;

FIG. 4 a format of an EGPRS downlink RLC data block header for MCS-7,MCS-8, and MCS-9;

FIG. 5 a format of an EGPRS downlink RLC data block header for MCS-5 andMCS-6; and

FIG. 6 a format of an EGPRS downlink RLC data block header for MCS-1,MCS-2, MCS-3, and MCS-4.

METHOD USED WITH GPRS

To detect if a multiuser operation took place at the time of datatransmission,

-   -   both the RLC data blocks as well as the RLC/MAC control blocks        must be evaluated    -   for the entire lifetime of the respective uplink and/or downlink        TBF    -   on all timeslots allocated to the respective TBF (multislot        operation is possible!)    -   for all TBF's (internal and external!) existing at that time.

This means for the subscriber side measurement system that RLC blocksthat do not belong to the internal TBF cannot be disregarded.

The analysis/evaluation system and the corresponding software mustinclude all corresponding information in the analysis, i.e., not onlythe information belonging to the examined TBF.

Because cells change during a mobile data transmission, this aspect mustbe taken into consideration in the analysis. Changes in multislotoperation as well as in multiuser behavior can be expected after cellchanges.

According to the Standard, the function “Delayed TBF” is provided, whichis implemented differently depending on the system design and dependingif this is an uplink or a downlink.

The contents of the RLC blocks are so-called “Dummy Blocks.”Counting/evaluation in the internal TBF must therefore conclude with thetransmission of useful data.

Requirements for Detecting the Situation in the Uplink (Subscriber-SideMeasurement System)

The network side distributes/allocates the RLC blocks for the Uplink.The currently employed allocation method is the dynamic allocationmethod. In this allocation method, the Uplink State Flag (USF) informsthe ME about the RLC blocks to be used for the existing TBF.

The USF is located in the MAC header in each RLC data block and in eachRLC/MAC control block of the downlink.

The downlink RLC data block together with its MAC header has the formatshown in FIG. 2. The USF is described by the first three bits in the MACheader.

The downlink RLC/MAC control block together with its MAC header isillustrated in FIG. 3. The USF is here also described by the first threebits in the MAC header.

Within the context of the TBF establishment-process, a certain USF isassociated with a UL-TBF.

For the duration of a UL-TBF, the measurement systems must determine forthe timeslots occupied by the TBF, if the network side has allocatedother USF's besides those belonging to the established UL-TBF.

The following statements can be made in the context of themeasurement/evaluation:

-   -   In general, did a multiuser operation take place?    -   Which timeslots are affected by this multiuser operation?    -   How many parallel users were in each timeslot?        Which is the ratio of the number of the internally used RLC        blocks to the number of the externally used RCL blocks or to the        total number of RLC blocks in the TBF time period?

Requirements for Detecting the Situation in the Downlink(Subscriber-Side Measurement System)

The network side allocates the RLC blocks for the downlink.

In multiuser operation, allocation methods are specific to the employedsystem design.

A different parameter from the two possible RLC downlink blocks must beevaluated for detecting the behavior in the downlink.

This is the TFI, which is uniquely associated with a (TL-) TBF duringthe assignment.

Unlike the USF, this parameter is not included in the MAC header, butcan instead be included in the RLC header, where it occupies the bits2-6 in the first octet. Alternatively, it can be included in the RLC/MACcontrol block, where it occupies the bits 2-6 in the second octet.

As long as data transfer in the DL continues, the ME is required toevaluate each RLC-DL block to determine if this RLC block is intendedfor the corresponding TBF/TFI. If this is not the case, then this RLCblock would be disregarded by the MS.

Within the context of the measurement/evaluation process, it can thenagain be determined:

-   -   In general, did multiuser operation occur?    -   Which timeslots are affected by this multiuser operation?    -   How many parallel users were in each timeslot?        Which is the ratio of the number of the internal the used RLC        blocks to the number of the externally used RCL blocks or to the        total number of RLC blocks in the TBF time period?

Method Used With Egprs

In general, the same basic principles apply to EGPRS as to GPRS.

The EGPRS data blocks include a RLC/MAC header which contains thecorresponding information. Unlike with GPRS, the header format andheader types are different depending on the employed modulation andcoding schemes (MCS). A differentiation is made between the modulationand coding schemes MCS-1 to MCS-9.

The combined EGPRS downlink RLC/MAC header for the modulation and codingschemes MCS-7, MCS-8, and MCS-9 (header type 1) has the formatillustrated in FIG. 4.

The combined EGPRS downlink RLC/MAC header for the modulation and codingschemes MCS-5 and MCS-6 (header type 2) has the format illustrated inFIG. 5.

The combined EGPRS downlink RLC/MAC header for the modulation and codingschemes MCS-1, MCS-2, MCS-3, and MCS-4 (header type 3) has the formatillustrated in FIG. 6.

In all header types, the USF is located in the first three bits of thefirst octet. The TFI includes the first 4 bits of the second octet.

The analysis of the multiuser operation is performed analogous to thatfor GPRS for the uplink by evaluating the Uplink State Flags (USF) andfor the downlink via the Temporary Flow Identifier (TFI).

An example of possible triggering of a data acquisition and evaluationis described below (the description applies to both the subscriber sideand the network side):

Triggering for the Uplink

The “classic” setup of an uplink TBF is performed via RACH and PRACH.

The relevant messages are:

-   -   CHANNEL_REQUEST (for GPRS /on RACH)    -   PACKET_CHANNEL_REQUEST (for GPRS /on PRACH)    -   EGPRS_PACKET_CHANNEL_REQUEST (for GPRS /on RACH or PRACH)

If only the application-controlled data transfer is to be analyzed, thenthe following information elements (IE) from the above-mentionedmessages have to be considered:

-   -   Two Phase Access Request and/or Single Block Packet Access    -   Short Access Request

In EGPRS, the resource request is different depending if a channel withor without 8-PSK modulation is to be provided.

Those RLC data blocks are then relevant for the evaluation, which aretransmitted starting with the time, timeslot, and frame specified in themessage

PACKET_UPLINK_ASSIGNMENT.

The resource request via the channel: PACCH forms another category.

The relevant message is:

-   -   PACKET_DOWNLINK_ACK/NACK with the IE: Channel Request        Description.

Resources are allocated by the messages:

-   -   PACKET_UPLINK_ASSIGNMENT or PACKET_TIMESLOT_RECONFIGURE.

If “Fixed Allocation” is used in the network, then resources can also beallocated by the message PACKET_UPLINK_ACK/NACK.

The RLC data block, at which the countdown value reaches the value “0”and the transmission/decoding of this RLC block is confirmed with anACK-message from the network side, is regarded as end point fortriggering.

Triggering for the Downlink

Like for the uplink, a “classic” variant exists: by paging.

The relevant messages are here:

-   -   PAGING_REQUEST (via PCH)    -   PACKET_PAGING_REQUEST (via PPCH)

Relevant for the evaluation are then those RLC data blocks, which aretransmitted starting with the time, timeslot, and frame specified in themessage

PACKET_DOWNLINK_ASSIGNMENT.

If the MS is in the READY State, then the allocation is made only withthe message:

-   -   PACKET_DOWNLINK_ASSIGNMENT.

Allocation is also feasible via PACCH with the message:

-   -   PACKET_TIMESLOT_RECONFIGURE.

The RLC data block, at which the “Final Bit” is set andtransmission/decoding of this RLC block is confirmed with an ACK-messagefrom the network side, is regarded as end point for triggering.

The measurement system supports the obtained results with dedicatedanalyses and evaluations (statistics and visualizations, optionally formultislot, multiuser and/or multi-usage).

LIST OF REFERENCE SYMBOLS AND ABBREVIATIONS

-   -   1 SGSN Serving GPRS Support Node    -   2 MSC Mobile Switching Center    -   3 GMSC Gateway Mobile Switching Center    -   4 PSTN Public Switched Telephone Network    -   5 GGSN Gateway GPRS Support Node    -   6 Internet    -   7 Intranet    -   8 PCU Packet Control Unit    -   9 BSC Base Station Controller    -   10 BTS Base Transceiver Station    -   11 ME Mobile end station    -   AUC Authentication Center    -   BSS Base Station Subsystem (BTS+BSC+PCU)    -   DL Downlink    -   EGPRS Enhanced GPRS    -   GPRS General Packet Radio Service    -   GSN GPRS Support Node    -   HLR Home Location Register    -   LLC Logical Link Control    -   MAC Medium Access Control    -   MCS Modulation and Coding Scheme    -   PSS Packet Switched Subsystem    -   RLC Radio Link Control    -   TBF Temporary Block Flow    -   TFI Temporary Flow Identifier    -   UL Uplink    -   USF Uplink State Flag    -   VLR Visitor Location Register

1-20. (canceled)
 21. A method for detecting multiuser behavior on anaerial interface in GPRS and EGPRS mobile radio systems, comprising thesteps of acquiring and evaluating during a transmission of subscriberdata on an aerial interface, additional information contained insubscriber data by a device on a network side and/or a subscriber side,both in the uplink and the downlink.
 22. The method according to claim21, further comprising the steps of comparing at the beginning of aTemporary Bit Flow (TBF) the number of the used Radio Link Control (RLC)blocks with an actually available and hence usable number of RLC blocks,and identifying a number of parallel subscribers in used timeslots basedon the additional information contained in the RLC blocks.
 23. Themethod according to claim 21, further comprising the step of evaluatingparameters Uplink Status Flag (USF) and/or Temporary Flow Identifier(TFI) as additional information.
 24. The method according to claim 23,further comprising the step of determining for the duration of an uplinkTBF, how many USF's are allocated by the network side.
 25. The methodaccording to claim 23, further comprising the step of determining forthe duration of a downlink TBF, how many USF's are allocated by thenetwork side.
 26. The method according to claim 23, further comprisingthe step of identifying the USF's and/or TFI's and for each TBF and acombination of all TBF's which are part of the transfer.
 27. The methodaccording to claim 22, further comprising the step of determining, in astatic allocation process, the usage of the timeslots for the RLC blocksby counting the data frames.
 28. The method according to claim 21,further comprising the step of evaluating for the entire lifetime of therespective uplink TBF and/or downlink TBF, the RLC data as well as theRLC/MAC control blocks for all TBF's in existence at that time and inall timeslots allocated to the respective TBF, and determining based onthese data if a multiuser operation has occurred at the time of the datatransmission.
 29. A device for detecting multiuser behavior on theaerial interface in GPRS and EGPRS mobile radio systems, wherein duringa transmission of subscriber data on the aerial interface, additionalinformation contained in the subscriber data are acquired and evaluatedby at least one device on the network side and/or the subscriber side,both in the uplink and the downlink and wherein the at least one devicefor acquiring additional information is provided on the network sideand/or on the subscriber side in the mobile radio network, whichinformation is included in the subscriber data transmitted on the aerialinterface in the downlink and uplink.
 30. The device according to claim29, wherein the at least one device is provided in the Packet ControlUnit PCU (8).
 31. The device according to claim 29, wherein the at leastone device comprises a subscriber-side measurement system, whichcooperates with or is integrated in a mobile radio terminal.
 32. Thedevice according to claim 29, wherein the additional informationcomprises the parameters USF and/or TFI.